Ammonia is a basic raw material for producing such important chemical products as fertilizers, nitric acid, plastics, etc., and at the same time is a hydrogen source carrier with a potential application prospect; thus the ammonia synthesis and decomposition have a very important significance in industry. The direct catalytic conversion of N2 and H2 is a main means of industrial ammonia synthesis. Because the reaction condition of the ammonia synthesis is harsh and the requirement for a device is very high, the energy consumption is very high, and the annually consumed energy is 1% of the total annual energy consumption in the world. Recently, the catalysts widely used for ammonia synthesis and ammonia decomposition in industry are respectively transition metal catalysts such as Fe-based catalyst, Ru-based catalyst, Ni-based catalyst, etc. However, for decades, the efficiency of ammonia synthesis has not been improved and increased significantly, and the reaction condition still needs high temperature and high pressure. For an ammonia decomposition reaction, the low-cost Ni-based catalyst, however, shows low activity. Therefore, the development of a novel ammonia synthesis and ammonia decomposition catalyst system with low-temperature, low-pressure activity and high-efficiency is a very important research topic at present. Without the limitations of the Fe and Ru-based catalyst, the research and development of catalysts of other components by referring to an existing basic theory and technology is an effective strategy of developing a new generation of ammonia synthesis and ammonia decomposition catalyst.
As for a non-Fe(Ru)-based catalyst of ammonia synthesis and decomposition, some progress has been made in recent years. Aika and Jacobsen et al. respectively reported that a transition metal nitride alloy shows good catalytic activity in ammonia synthesis. Under lower temperature and pressure, the activity of a Cs-promoted Co3Mo3N catalyst is superior to that of an industrially widely used multiply-promoted fused iron catalyst, and under certain condition, even is superior to that of the Ru-based catalyst [R. Kojima, K. Aika, Chem. Lett., 2000, 514-515; C. J. H. Jacobsen, Chem. Commu., 2000, 1057-1058.]. C. Li et al. used the transition metal nitride alloy supported on aluminium oxide in the ammonia decomposition reaction, and also obtained better catalytic activity [C. H. Liang, W. Z. Li, Z. B. Wei, Q. Xin, C. Li, Ind. Eng. Chem. Res., 2000, 39: 3694-3697.].
Ohtsuka et al. used calcium oxide supported on carbon-based materials in the decomposition reaction of ammonia of a low concentration (2000 ppm), and found that the catalyst shows certain catalytic ammonia decomposition activity above the temperature of 700° C. [Y. Ohtsuka, C. Xu, D. Kong, N. Tsubouchi, Fuel, 2004, 83: 685-692.].
In conclusion, the non-Fe(Ru)-based ammonia synthesis and ammonia decomposition catalyst has made some progress, but also is unable to achieve industrialization. Further study shall be made on how to regulate the catalyst composition and structure to enhance the activity and stability of the catalyst and reduce catalyst cost.